The use of towed vehicles, such as trailers has become increasingly popular in recent years. Particularly, the use of towed vehicles in tandem is popular. Tandem towing allows two or more vehicles to be towed by a single power vehicle such as a truck tractor. Highway trailers generally include one or more fixed rear axles and wheels that provide support for the trailer but can not be turned or steered. The front portion of a highway trailer typically includes a "fifth wheel," which allows the highway trailer to be releasable secured to and supported by the towing vehicle or truck tractor. A fifth wheel arrangement, which is common in the art and is described in U.S. Pat. No. 5,407,221, entitled Converter Dolly, supports the towed vehicle independent of the tractor and allows the towed vehicle to pivot relative to the towing vehicle and follow the tractor through turns. Highway trailers are frequently connected in tandem by a dolly having one or more axles and wheels appropriate for highway transportation.
A major problem that occurs in towing tandem trailers with a converter dolly is backing up the towed vehicles. While backing up, the towed vehicles will tend to move in the opposite direction of the tractor, causing "jackknifing" of the towed vehicles and making extremely difficult backing up of tandem trailers. Because of this problem, trailers in a tandem arrangement often must be disconnected from the converter dolly, connected to the tractor, and backed up individually. Backing up an individual trailer suffers from the same difficulties discussed above but to a lesser degree than backing up a tandem arrangement of trailers. Disconnecting the tandem arrangement and backing up each trailer individually increases delay and expense.
One attempt at solving the problem of backing up is described in U.S. Pat. No. 5,407,221, entitled Converter Dolly for Permitting Backing Up of Tandem Trailers. The system described in the '221 Patent uses a two-part pivoting frame for the dolly to facilitate movement in the reverse direction and utilizes the fifth wheel to facilitate steering in the forward direction.